The present invention relates to a transporting system of floated carrier type for transporting small cargo and, more particularly, to a transporting system of floated carrier type capable of reducing an impact acting on a carrier itself or cargo loaded thereon when the carrier is ceased to be floated.
As one method of office automation, a carrier system has been recently widely used to transport slips, documents, cash, materials, and the like between a plurality of stations in a building.
A carrier system used for such an application must be able to transport cargo rapidly without noise. For this reason, in a carrier system of this type, a carrier is generally suspended under and transported along guide rails in a noncontacting manner. A system of magnetically suspending or floating a carrier in a noncontacting manner has advantages such as a good following property with respect to guide rails and an effect of preventing noise and dust.
However, in a system wherein a carrier is floated by a magnetic force, when all the magnetic force as a floating force is to be supplied from electromagnets, the electromagnets must always be energized, resulting in a large current consumption. Therefore, the present inventor has proposed a so-called zero power feed-back control system (U.S. Ser. No. 06/726,975, filed Apr. 25, 1985, now abandoned) in which most of the magnetic force, supplied from the electromagnets, is supplied by permanent magnets, thereby reducing the power consumption.
However, in such a magnetic floating system, since a floating carrier is not fixed by a friction force, the carrier may be shaken during cargo loading/unloading at a station, resulting in a difficult loading/unloading operation. In addition, sometimes a floating state of the carrier cannot be maintained due to rolling produced by loading/unloading operation. A stopper may be provided at a station to fix the carrier so that the floating carrier is not shaken. However, such a stopper must not contact the carrier when the carrier simply passes through the station, thereby rendering a mechanism around the station complex in structure.
Therefore, the carrier may be attracted to be fixed on the guide rails or land on auxiliary rails during the loading/unloading operation. However, in a transporting system of floated carrier type adopting zero steady-state power feed-back control (also referred to hereinafter as "zero power feed-back control), an exciting current supplied to a magnetic unit is controlled to be normally zero i.e., zero in the steady-state. Therefore, unlike a conventional magnetic floating control without a zero power feed-back loop, even if a target value of a gap length between the guide rails and the electromagnets is varied, an actual gap length cannot be varied because it is uniquely determined by the weights of the carrier and the cargo. For this reason, in order to, e.g., attract the carrier on the guide rails, power sources of the electromagnets and a control circuit must be turned off during magnetic floating.
However, when the power sources of the electromagnets and the control circuit are turned off during magnetic floating of the carrier, a large impact occurs between the guide or auxiliary rails and the carrier, thereby undesirably destroying the cargo or the carrier or generating dust.
Thus, in the conventional transporting system of floated carrier type adopting zero power feed-back control, the carrier cannot be fixed to the guide rail or released from the guide rail without the large impact between the guide or auxiliary rails and the carrier when the landing or floating of carrier is started, thereby undesirably destroying the cargo or the carrier or generating dust.